The Toxicity of Hydrogen Peroxide to Rainbow Trout Oncorhynchus mykiss and Cutthroat Trout Oncorhynchus clarki Fry and Fingerlings

Fungal and parasitic infections of fish can significantly impact the survival of cultured fish. Formalin is currently used to control such infections; however, concern has arisen over its safety to users and to the environment. Hydrogen peroxide has been designated as a low priority fungicidal drug by the United States Food and Drug Administration (FDA), yet, little information is available on treatment concentrations or its toxicity to trout. Rainbow trout Oncorhynchus mykiss and cutthroat trout Oncorhynchus clarki fry and Angerlings were exposed to hydrogen peroxide concentrations of 0, 70, 170, 280, 420 and 540 ppm for 30, 60 or 120 rnin at 15 C to determine the chemical's toxicity. Rainbow trout fry and fingerlings experienced elevated mortalities (>20%) during treatments using 420 and 540 ppm for 30 min; 280, 420 and 540 ppm for 60 min; and >170 ppm for 120 min. Cutthroat trout fry experienced elevated mortalities (>23%) during treatments using 540 ppm for 30 min; 420 and 540 ppm for 60 min; and >170 ppm for 120 min. Cutthroat trout fingerlings experienced elevated mortalities (>60%) during treatments using 540 ppm for 60 min and >280 ppm for 120 min. No control mortalities were encountered for both life stages of either species. The lethal concentrations (LC₅₀) of both age classes and species for each of the three durations ranged from 514–636 ppm for 30 min treatments, 322–506 ppm for 60 min treatments, and 189–280 for 120 min treatments. Mortalities for all four toxicity tests which occurred during a 96-h post-treatment period were centered around the following treatments: 30 min, 540 ppm; 60 min, 280–540 ppm; 120 min, 170 ppm. Tissue damage to gills was found only among fish that did not survive the initial chemical exposure. Test concentrations proved to be relatively stable during a 24-h period, retaining better than 85% of their original strength for all five dilutions. At a water temperature of 15 C concentrations should not exceed 280 ppm for a 30-min treatment.     

Toxicity of chlorine to different sizes of black tiger shrimp (Penaeus monodon) in low-salinity shrimp pond water

An experiment was conducted, in a dark room with controlled temperature (27.3–28.4 °C), to determine the acute toxicity of chlorine concentration to black tiger shrimp (Penaeus monodon fabicus) of sizes 0.02 g, 2.75 g, 8.47 g and 23.65 g. Toxicity tests on each of these shrimp sizes were run in triplicate in glass jars under static conditions without media renewal. The concentration of active chlorine that killed 50% of the shrimp of each size after 24‐h exposure (LC₅₀‐24 h) was used as an indicator of acute toxicity. Chlorine concentrations applied in the shrimp toxicity test ranged from 2.0 to 14.5 mg L^?1 in shrimp pond water. As the test water contained total suspended solids of 22.0–85.0 mg L^?1 and total ammonia nitrogen of 0.18–0.40 mg L^?1, the resultant concentrations of combined residual chlorine ranged from 0.6 to 3.5 mg L^?1, which were the effective doses causing shrimp mortality. The test results showed that 24‐h LC₅₀ for average shrimp size at 0.02, 2.75, 8.47 and 23.65 g occurred in water containing combined residual chlorine at a concentration of 0.91, 1.39, 1.74 and 1.98 mg L^?1, for which the original application doses were 6.96, 2.05 11.50 and 13.34 mg L^?1 respectively.     

Investigations on the effect of formalin and iodophor on embryo and larvae development in pikeperch,Sander lucioperca

ABSTRACT

An experiment was conducted to evaluate the effects of incubating pikeperch, Sander lucioperca, eggs in formalin and iodophor solutions for 15 min on embryo survival, the hatching rate, as well as on the rate of misshaped larvae, in order to develop methods for egg surface disinfection. Embryos in the morula stage, in the epiboly stage, and at the beginning of heart beat and blood circulation tolerated formalin concentrations up to 1,500 ppm for 15 min. However, they were very susceptible to iodophor treatment, as >0.1% iodophor solution (=13 ppm active iodine) significantly decreased the percentage of ready-to-hatch embryos and the percentage of hatched larvae. These data of this study recommend the use of formalin at a concentration of up to 1,500 ppm to disinfect pikeperch eggs.     

A method for collecting eggs of Pseudocapillaria tomentosa (Nematoda: Capillariidae) from zebrafish Danio rerio and efficacy of heat and chlorine for killing the nematode's eggs

Pseudocapillaria tomentosa is a common pathogen of zebrafish (Danio rerio) in research facilities. We developed a method to collect and concentrate the nematode eggs using a modified sugar centrifugation method and documented their normal development. Embryonating stages with blastomere formation followed by elongation of the embryo prior to larva formation cumulated in developed larvae inside the eggs and hatching after 5–10 day. We then evaluated the efficacy of heat and chlorine to kill them based on a larva development assay. Eggs were exposed to 40, 50, 60 °C for 30 min and 1 h. Chlorine treatment was performed at 100, 250, 500, 1000, 3000 and 6000 ppm for 10 min. Samples exposed to 40 °C for 30 min or 1 h showed incidences of larvated eggs similar to controls. In contrast, no larvation occurred with eggs exposed to either 50 or 60 °C for 30 min or 1 h. Remarkably, in repeated assays, samples exposed to low doses of chlorine (100, 250, 500 and 1000 ppm for 10 min) showed significantly higher incidence of larvation than controls. Eggs treated with 3000 ppm for 10 min did not develop larvae, and no eggs were found after 6000 ppm treatment.     

Factors influencing the efficacy of MS-222 to striped mullet (Mugil cephalus)

Some responses of juvenile striped mullet (Mugil cephalus) to the anesthetic MS-222 were investigated. Induction times to total loss of equilibrium decreased with increasing anesthetic concentration over the range of 40–120 ppm. Temperature, pH, and oxygen concentrations all significantly affected induction times to total loss of equilibrium in freshwater-adapted fish at a concentration of 80 ppm MS-222. Anesthetic toxicity was less for saltwater-acclimated fish than for freshwater-acclimated fish. The 24-h 50% mortality (LC₅₀) in fresh water was 33.1 ppm; in salt water it was 39.8 ppm. The results suggest that anesthetic action may be intensified in fish acclimated to conditions other than those near their physiological optima.     

Roles of water quality and disinfectant application on inactivation of fish pathogenic Streptococcus agalactiae with povidone iodine,quaternary ammonium compounds and glutaraldehyde

Streptococcosis is an important bacterial disease in Nile tilapia causing severe economic losses to tilapia aquaculture worldwide. The effects of water quality (low‐ [LS] and high‐level [HS] soiling, to mimic clean or dirty surface conditions and temperatures) and disinfectant application (diluted concentrations and exposure time) were characterized on the inactivation of Streptococcus agalactiae isolated from diseased tilapia. Five isolates were tested against three commercial disinfectant products with the main ingredients being povidone iodine (Anidine 100?; AD), benzalkonium chloride (Better BKC 80%?; BKC 80), and a mixture of quaternary ammonium compounds and glutaraldehyde (Chloraldehyde?; CR). CR demonstrated highest efficacy to S. agalactiae inactivation, followed by BKC 80 and AD, respectively. Higher‐level soiling, low temperature, diluted concentrations and short exposure time all decreased the disinfectant efficacy. CR and BKC 80 provided more than 5‐log inactivation at 1‐min exposure at 20°C under HS conditions, and also with ten‐fold‐diluted concentrations at 60‐min exposure time at 30°C. However, AD required 10‐min exposure to effectively remove bacteria under LS conditions at 30°C. The results could facilitate aquaculture management planning that leads to operating cost reductions and improvements in biosecurity.     

Environmental persistence of chlorine from prawn farm discharge monitored by measuring the light reactions of photosynthesis of phytoplankton

Chlorine (reactive chlorine: Cl₂+OCl^?) is used as a disinfectant on prawn farms but the environmental effects of discharged chlorine is of environmental concern. Toxicity of chlorine on prawn farm phytoplankton populations was monitored using the pulse amplitude fluorometer technique to measure phytoplankton photosynthesis. The dominant phytoplankton species found in the ponds of a prawn farm in Pang-Nga Province (Thailand) were Chlorella sp. (>95 %), with some Tetraselmis and Chaetoceros. Cells were suspended in clean sea water with (chlorine) of 15, 30, 45, 60, 75 and 90 ppm, respectively, in short-term experiments for 10 min (ST) and for long-term (24 h) exposure. Photosynthesis of Chlorella, Tetraselmis and Chaetoceros in clean sea water was inhibited by 50 % at (chlorine) of 4.68 ± 0.6, 7.26 ± 1.14 and 7.81 ± 0.78 ppm (mean ± SEM), respectively, in ST experiments. The chlorine consuming reactions with the large amounts of dissolved organic matter and ammonia in prawn farm pond water decreases toxicity but would form organochlorines and chloramine. Thiosulphate, often used to neutralise chlorine, was found to be of very limited toxicity to Chlorella in both short-term 1-h and 24-h experiments (up to ≈500 mmol m^?3, 124 ppm). Environmental effects of Chlorine in discharges from ponds are short term. Chlorine quickly disappears in the environment, particularly during daylight and so only has effects close to effluent points. Standard practice was to discharge on a falling tide in daylight. The long effluent channel (1 km) also ensured that very little reactive chlorine reached the estuary.     

Effect of iodophor disinfection of non‐hardened Salmo trutta eggs on their bacterial and fungus load

This study investigated the efficiency of iodophor disinfection (135 ppm active iodine for 15–30 min) of non‐hardened Salmo trutta eggs against different groups of bacteria and against fungus. Egg samples were taken from non‐disinfected and from disinfected eggs, microorganisms were cultured on specific nutrient media and their mass was measured by turbidimetric methods. Bacteria and fungus mass of non‐hardened eggs could be reduced but not eliminated by iodophor disinfection with 135 ppm active iodine for 15 min. The extent of reduction was 47–65% (Experiment 1). The efficiency of disinfection increased with disinfection time as the reduction in bacteria and fungus mass was 40–55% after 15 min and 58–74% after 30 min (Experiment 2). Disinfection efficiency of iodophor solution diluted in water (reduction 49–57%) and of iodophor solution diluted in sodium chloride solution iso‐osmolar to the oocytes (reduction 52–61%) was similar (Experiment 3). The reduction in bacteria and fungus mass was persistent as it was 39–72% lower in embryos deriving from disinfected eggs than in embryos deriving from non‐disinfected ones (Experiment 4). In conclusion, the tested disinfection method is inadequate to eliminate pathogens completely but it could positively influence immune defence of eggs and embryos.     

Virucidal effects of common disinfectants against tilapia lake virus

Tilapia lake virus (TiLV) is an emerging virus associated with high fish mortality and economic losses. This study investigates the virucidal effects of the following disinfectants (active ingredients) on TiLV: 2.5 ppm iodine, 10 ppm sodium hypochlorite (NaOCl), 300 ppm hydrogen peroxide (H₂O₂), 80 ppm formalin and 5,000 ppm (0.5%) Virkon^®. Factors that affect the disinfectants’ efficacy, including temperature, contact time and soiling (organic matter) interference, were examined under conditions mimicking natural aquaculture practices. TiLV inactivation of higher than 5 log₁₀ TCID₅₀ ml^?1 was achieved after 10 min and at 28°C for all disinfectants except formalin; similar inactivation levels were reached by NaOCl and Virkon^® at 10 min and 4°C. Extended exposure to formalin from 10 to 60 min at 28°C rendered more than 5 log₁₀ inactivation. Increasing synthetic organic matter in the water to mimic soiling interference reduced the efficacy of NaOCl, iodine and H₂O₂ when tested at 10 min and 28°C; however, Virkon^® still achieved more than 5 log₁₀ inactivation. This study demonstrates that most common disinfectants effectively reduced viral loads to minimum levels. To limit the spread of TiLV in aquaculture farms and related facilities, the appropriate use of such disinfectants should therefore be promoted and implemented.     

An evaluation of three potential methods for preventing the spread of larval Lepeophtheirus salmonis (Krøyer, 1837)

Within the State of Maine, only a portion of the farm sites experience sea lice (Lepeophtheirus salmonis) infections on an annual basis. There has been concern about the further spread of lice by farming activities to unaffected areas despite routine disinfection of equipment with sodium hypochlorite or iodophors. We examined the effects of Povidone‐iodine, sodium hypochlorite and desiccation on egg strings of L. salmonis and the potential of these methods for preventing hatching of nauplii or development to the copepodid stage. L. salmonis egg strings were exposed to one of eight treatments: 200 ppm of sodium hypochlorite or Povidone‐iodine solutions for 1 min, 500 ppm of either disinfectant for one minute or 10 min, or desiccation for either 4 or 24 h. The egg strings were then incubated and the hatched copepods were kept for 6 days in filtered natural seawater at 32 ppt salinity at 12°C. Desiccation for 4 or 24 h were the only methods that prevented L. salmonis nauplii from hatching or developing to the infective copepodid stage. Common disinfection procedures against pathogenic bacteria and virus were not found to be effective against L. salmonis eggs.     

Optimization of Ozonated Water Treatment of Wild-Caught and Mechanically Peeled Shrimp Meat

ABSTRACT

Ozone is a USFDA and USDA approved food contact sanitizing agent and has been used in the seafood industry in both gaseous and dissolved forms to destroy bacteria. The wild harvest shrimp industry is the most economically important fishery in the U.S. Gulf of Mexico region, and in Louisiana the majority of the harvest is mechanically peeled and frozen. Dissolved ozone was measured in processing water at product application to study the optimization of ozonated water treatment for reducing microbial contamination of peeled shrimp meat. Shrimp samples were either sprayed or soaked in water with 1, 2, and 3 ppm dissolved ozone. Treatment times of 20, 40, and 60 seconds were investigated for all applications and concentrations. Similar volumes of water were applied for all treatments, and soaking showed greater bacterial reduction than spray treatments for all time and concentration combinations studied. Soaking in 3 ppm dissolved ozone for 40 s and 60 s showed the greatest reduction of total aerobic bacteria, and 60 s at 3 ppm resulted in the greatest reduction of Pseudomonas bacteria. Ozonated water treatment did not produce oxidation in the shrimp samples. The optimal treatment of soaking shrimp in 3 ppm dissolved ozone for 60 s will be used for further investigations of refrigerated shelf life extension and Listeria monocytogenes destruction in peeled shrimp meat.     

Ichthyophonus‐infected walleye pollock Theragra chalcogramma (Pallas) in the eastern Bering Sea: a potential reservoir of infections in the North Pacific

In 2003, the Alaska walleye pollock industry reported product quality issues attributed to an unspecified parasite in fish muscle. Using molecular and histological methods, we identified the parasite in Bering Sea pollock as Ichthyophonus. Infected pollock were identified throughout the study area, and prevalence was greater in adults than in juveniles. This study not only provides the first documented report of Ichthyophonus in any fish species captured in the Bering Sea, but also reveals that the parasite has been present in this region for nearly 20 years and is not a recent introduction. Sequence analysis of 18S rDNA from Ichthyophonus in pollock revealed that consensus sequences were identical to published parasite sequences from Pacific herring and Yukon River Chinook salmon. Results from this study suggest potential for Ichthyophonus exposures from infected pollock via two trophic pathways; feeding on whole fish as prey and scavenging on industry‐discharged offal. Considering the notable Ichthyophonus levels in pollock, the low host specificity of the parasite and the role of this host as a central prey item in the Bering Sea, pollock likely serve as a key Ichthyophonus reservoir for other susceptible hosts in the North Pacific.     

Use of alternative disinfectants, individually and in combination, in aquacultural wastewater treatment

The inactivation effect of chlorine, iodine, ozone and UV irradiation was compared between phosphate buffered saline and waste water collected from a fish farm, with the fish-pathogenic bacterium Aeromonas salmonicida subsp. salmonicida as the model organism. In addition, the effect of combining chlorine, iodine or ozone with UV was evaluated. A tenfold increase in initial chlorine concentration, from 0.2 to 2.0 mg l^?1. had to be applied to maintain the same level of inactivation in waste water as in PBS. Iodine was less efficient than chlorine in PBS. by demanding a concentration of 1.0 mg l^?1 to obtain the same rate of inactivation as with 0.2 mg l^?1 chlorine. However, no difference between the two halogens was evident in the low-quality water. An initial ozone concentration of 0.1 mg l^?1 in PBS caused a rapid drop in bacterial viability for the first 20 s after which the curve levelled off. By continuous ozonation of waste water, a residual oxidant concentration of about 0.3 mg l^?1 had to be established before a rapid inactivation was observed. The UV inactivation profiles in PBS and waste water were almost identical, with a 99.9% reduction in viability after 48 and 50 s. respectively. When UV irradiation was combined with chlorine, a less than additive effect, as compared with the sum of individual death rates by the two treatments, was observed. The corresponding UV/iodine combination at least gave an additive effect in both water qualities. No increment in inactivation rate in PBS was observed when ozone was used in combination with UV, as compared with ozone alone.     

Instantaneous effect of dibromomethane on metamorphosis of larvae of the sea urchins Strongylocentrotus nudus and Strongylocentrotus intermedius

A volatile chemical, dibromomethane (DBM), produced from red coralline algae is known as a chemical inducer of larval metamorphosis of the sea urchin Strongylocentrotus nudus. We performed experiments exposing DBM to the larvae of S. nudus and Strongylocentrotus intermedius through a hydrophobic membrane. Metamorphic rates resulting from different diluted DBM solutions and exposure times were ascertained. The highest metamorphic rate, more than 80% in both species, was found after 1 h exposure to 1/2 diluted DBM. With this dilution, more than 80% of S. nudus and S. intermedius larvae metamorphosed 1 h after start of the experiment after only 10 and 5 min exposure, respectively, which corresponded to the low concentrations of 52–61 ppm and 34–43 ppm DBM by GCMS analysis, respectively. These findings suggest that DBM has an instantaneous effect on high success of metamorphosis of larvae of S. nudus and S. intermedius.     

Anaesthetic effect of eugenol at different concentrations and temperatures on black tiger shrimp (Penaeus monodon)

The anaesthetic effects of eugenol on Penaeus monodon were investigated at the different eugenol concentrations (60, 110, 160 and 210 mg/L), water temperature (21, 26 and 31°C), air exposure time (3, 6, 9 and 12 min) and body weight (2.62 ± 0.27, 6.34 ± 0.36 and 11.43 ± 0.33 g). The anaesthesia and recovery time were recorded. The results showed that the anaesthesia time of the shrimp decreased with the increase in the eugenol concentration and water temperature, and the recovery time increased with the increase of the eugenol concentration and the decrease of water temperature. Under the same eugenol concentrations, the recovery time increased with the increase of air exposure time and body weight. Under the eugenol concentration range of 60–210 mg/L, the recovered rate was 100%. The results indicated that eugenol is a safe and efficient anaesthetic for P. monodon.     

Effects of formalin on haematological and blood chemistry in olive flounder, Paralichthys olivaceus (Temminck et Schlegel)

Erythrocytes of olive flounder, Paralichthys olivaceus (Temminck et Schlegel), were treated with serial concentrations of formalin (37% formaldehyde) to investigate in vitro haemolysis and methaemoglobin formation. In addition, the short‐term toxicity of formalin concentrations of 0, 100, 212 and 300 ppm was also studied by clinical tests in which fish were subjected to 3‐h bath exposure. There was no haemolysis of fish erythrocytes exposed to formalin concentrations ranging from 31.3 to 2000 ppm. Methaemoglobin formation, however, was induced at concentrations greater than 500 ppm. Red blood cell count, haemoglobin, haematocrit, mean corpuscular haemoglobin concentration and percentage of immature erythrocytes were also markedly elevated in all formalin‐exposed groups (P<0.05). Formalin exposure also caused significant increases in alkaline phosphatase, aspartate aminotransferase, lactate dehydrogenase, potassium, chloride, magnesium and inorganic phosphorus (P<0.05). However, total protein decreased significantly in the formalin‐exposed groups (P<0.05). No significant differences in white blood cell count, mean corpuscular volume, mean corpuscular haemoglobin, albumin, glucose, total cholesterol, high‐density lipoprotein cholesterol, free cholesterol, alanine aminotransferase, calcium, creatinine and total bilirubin were observed in the formalin‐exposed groups (P>0.05).     

Surface disinfection of eggs from marine fish: evaluation of four chemicals

For surface disinfection of marine fish eggs Buffodine (1.06% free iodine), glutaraldehyde, chloramine-T and sodium hypochlorite (5% free chlorine) were tested using plaice (Pleuronectes platessa L.) as the main species for evaluation. Glutaraldehyde was the most promising candidate of the four chemicals tested. Good bactericidal effects without any documented negative effects on eggs and larvae were obtained at concentrations of 400–600 mg l^–1 and contact times of 5–10 min. Replicated experiments under identical disinfection conditions revealed a clear correlation between the degree of successful surface disinfection and the initial bacterial load of the egg batch.     

Studies on the physiology of somatolactin secretion in red drum and Atlantic croaker

The effects of exposure to water of different salinities and calcium concentrations, and to various backgrounds and illuminations on somatolactin (SL) levels in juvenile red drum (Sciaenops ocellatus) were investigated using a recently developed red drum SL radioimmunoassay. Plasma SL concentrations were also monitored in wild-caught Atlantic croaker (Micropogonias undulatus) during gonadal recrudescence. No correlations were obtained between plasma SL concentrations and different salinities, external calcium concentrations or reproductive condition in these sciaenid fishes. Plasma SL concentrations remained low (<1 ng ml^-1) in red drum 1h, 1 day and 1 week after exposure to full strength seawater (salinity 37%, calcium 1290 ppm), half strength seawater (salinity 18%, calcium 744 ppm), fresh water (salinity 1%, calcium 260 ppm) or soft water (salinity 0%, calcium 0 ppm). Circulating levels of SL did not change significantly in wild-caught croaker at the onset of vitellogenesis. However, by the end of ovarian recrudescence (late-yolk globule stage), plasma SL levels were significantly lower than those observed in females with immature (perinucleolar) oocytes. In contrast, plasma SL levels showed marked differences in red drum exposed to various backgrounds and illuminations. Plasma SL was lower in red drum kept in a light background (<1 ng ml^-1) than in those kept in a black background or in the dark (1.4-6.9 ng ml^-1). The highest plasma SL concentration (4–30 ng ml^-1) was obtained in red drum kept in a black background without illumination. These results suggest that SL is involved in the adaptation of the red drum to various backgrounds and illumination levels. SL may not have an important role during the reproductive cycle and adaptation to water of different salinities and calcium concentrations in sciaenid fishes.     

Gill histopathological characteristics of Caspian roach (Rutilus rutilus caspicus) fingerlings treated with potassium permanganate and formalin

The aim of this study was to determine the gill histopathological characteristics of Caspian roach (Rutilus rutilus caspicus) fingerlings exposed to different concentrations of potassium permanganate (PM) and formalin (FO). The fish were exposed to different PM and FO concentrations over different periods: 1 ppm PM for 24 h (1‐P24), 2 ppm PM for 24 h (2‐P24), 5 ppm PM for 0.5 h (5‐P0.5), 10 ppm PM for 0.5 h (10‐P0.5), 10 ppm FO for 24 h (10‐F24), 20 ppm FO for 24 h (20‐F24), 40 ppm FO for 0.5 h (40‐F0.5) and 80 ppm FO for 0.5 h (80‐F0.5). After exposure, gill samples were collected for histological examination. The most frequent gill histopathological symptoms were hyperplasia and epithelial lifting. The order of the gill injury index (I_g.i) among the treatments was as follow: 1‐P24, 2‐P24 < 5‐P0.5, 40‐F0.5 < 10‐F24 < 10‐P0.5, 20‐F24, 80‐F0.5. Comparing the two agents, it is concluded that there is no significant difference in the gill damages between the agents during the short‐bath treatments. However, PM causes less pathological symptoms than FO during the long‐bath treatments. Comparing the bath durations, the agents showed different behaviours. PM‐treated fish showed significantly lower gill damage during the long‐bath compared to the short‐bath treatment; whereas, pathological symptoms of FO‐treated fish was dose‐dependent for each exposure period, separately. Overall, exposure of Caspian roach to PM, at the concentrations recommended for long bath, resulted in milder gill damages compared to FO.     

Changes of Non-Specific Immune Parameters in Rainbow Trout,Oncorhynchus mykiss,After Exposure to Antimicrobial Agents Used in Aquaculture

Changes of plasma lysozyme and serum bactericidal activity, ceruloplasmin, total plasma protein, serum glucose, hematocrit and leucocrit levels in rainbow trout (Oncorhynchus mykiss) were studied after exposure to formalin and chloramine-T, which are used in aquaculture as anti-ectoparasitic and antibacterial agents. Fish were exposed to formalin at a concentration of 250 ppm for 60 min and exposed to chloramine-T for 5 ppm for 3 h. The parameters were analyzed for rainbow trout exposed to formalin and chloramine-T soon after treatments and rainbow trout exposed to freshwater after 24 h (return) following the treatments. Plasma lysozyme activity decreased after exposure to formalin; however, it was not affected by chloramine-T exposure. Serum bactericidal activity reduced after both formalin and chloramine-T exposure and did not change after returning to freshwater. Ceruloplasmin and total plasma protein were not affected by both treatments. Serum glucose levels of exposed fish elevated and remained at higher levels during recovery period when compared to control values. Hematocrit values of fish exposed to formalin increased; however, no significant change was observed in fish exposed to chloramine-T. Leucocrit levels of fish treated with both formalin and chloramine-T were higher than that of controls.